During normal use, contact lenses are soiled or contaminated with a wide variety of compounds that can degrade lens performance. For example, a contact lens will become soiled with biological materials such as proteins or lipids present in the tear fluid and which adhere to the lens surface. Also, by handling of the contact lens, sebum (skin oil), cosmetics or other materials can soil the contact lens. These contaminants can affect visual acuity and patient comfort. Accordingly, it is important to remove any debris from the lens surface and to disinfect the lens for safe and comfortable use. A care regimen for contact lenses typically involves both disinfection and cleaning.
For disinfection, a lens care solution must contain one or more antimicrobial components. Presently, the two most popular disinfectant components are poly(hexamethylene biguanide), at times referred to as PHMB or PAPB, and polyquaternium-1. Lens care solutions with PHMB represent a significant improvement in patient comfort and antimicrobial effectiveness compared to most other known antimicrobial components. However, as with any antimicrobial component there remains a tradeoff between the concentration of the PHMB in the solution and the comfort experienced by the patient. Due to its wide commercial acceptance, extensive efforts have been directed to improve the antimicrobial efficacy or the comfort level to the patient by chemically modifying PHMB.
Those in the art have also focused on enhancing the biocidal efficacy of an ophthalmic composition by including a compound that enhances the biocidal efficacy of the antimicrobial component. The idea being that a relative decrease in the concentration of antimicrobial component would lead to a solution with a greater comfort profile.
The use of amino acids to enhance the antimicrobial efficacy of contact lens care compositions has previously been described. For example, U.S. Pat. No. 5,741,817 to Chowhan et al. describes a method of enhancing the antimicrobial efficacy of ophthalmic compositions with the addition of a low molecular weight amino acid to a composition that does not contain ethylenediaminetetraacetic acid or the salts thereof. The claim of enhanced antimicrobial efficacy was supported by stand-alone biocidal test data. Similar stand-alone biocidal data is presented in U.S. Pat. No. 6,806,243 to demonstrate that an ophthalmic solution containing at least one antimicrobial component in combination with at least one amino acid component and at least one acidic component has germicidal or preservative activity. PCT Publication No. 95/30414 also describes the use of one or more amino acids for improved preservative efficacy in aqueous ocular care solutions.
Despite the availability of various commercial contact lens care solutions, there is always a need to improve upon the performance of such solutions. These improved lens care solutions should be simple to use, be effective against a broad spectrum of microorganisms, be non-toxic to ocular tissues and provide a comfortable ocular environment to the patient.